1. Field of the Invention
This invention relates to ice makers and in particular to slab-type ice makers as may be utilized in commercial ice production.
2. Description of the Prior Art
One form of improved slab-type ice maker is shown in U.S. Pat. No. 2,682,155 of Russell W. Ayres et al, which patent is owned by the assignee hereof. As shown therein, a refrigerated evaporator plate is provided which is arranged to have water recirculated over the upper surface thereof to build up a slab of ice thereon. Upon completion of the buildup of the desired slab, the evaporator plate is suitably heated to disengage the slab and permit it to slide by gravity onto a network of resistance heating wires which melt through the ice, thereby dividing the slab into discrete ice bodies. The ice bodies are then collected in the subjacent storage bin from which they may be removed by the user in the conventional manner.
In the Donald F. Swanson U.S. Pat. No. 2,959,026 also owned by the assignee hereof, an improved means for determining the thickness of the ice slab formed on the evaporator plate is disclosed as comprising a sensing member supported above the evaporator plate so that when the ice builds up to the predetermined final desired thickness, a switch is operated to terminate the ice making cycle and initiate the heating cycle for releasing the slab from the plate. Upon release of the slab, the switch is restored to initiate a subsequent ice forming cycle.
Another patent owned by the assignee hereof is that of Oscar E. Wendt, U.S. Pat. No. 3,613,388. In the Wendt patent, a plurality of evaporator plates are provided for concurrently forming a plurality of ice slabs. The water is flowed seriatim over the respective plates and recirculated by suitable pump means. A control is provided for sensing the failure of a released slab to clear the lower end of the evaporator plate so as to at least partially obstruct the water flow.
A slab-type ice making apparatus is shown in U.S. Pat. No. 2,747,375 of Joseph R. Pichler as including means responsive to a drop in the pressure of the supply water to automatically discontinue operation of the ice maker. The means for sensing the thickness of the slab is disposed above the evaporator plate and is adjustably mounted so as to permit varying the thickness of the desired slab.
Stanley H. A. Thompson, in U.S. Pat. No. 3,039,278, shows a means for de-frosting refrigerating apparatus wherein the sensing of a frost buildup in the refrigerator is effected by means of thermistors connected in a Wheatstone bridge arrangement.
In U.S. Pat. No. 3,246,210, Jerome L. Lorenz shows an ice level control circuit utilizing thermistors installed in a storage bin. The thermistors are installed at different levels such that the lower thermistor may initiate an ice making cycle to bring the level of ice in the storage bin back to the level of the upper thermistor which effects a termination of the ice making cycle. The thermistors control an electromechanical relay for controlling operation of the compressor of the refrigeration means.
Reuben Wechsler et al, in U.S. Pat. No. 3,363,429, show a temperature control circuit for a refrigeration system utilizing thermistors in sensing a frost condition in the refrigerator.
Donald E. Neill, in U.S. Pat. No. 3,721,880, shows a refrigeration system compressor motor control utilizing a thermistor and thermostat having contacts providing suitable signals to transistor elements of the control which function as low threshold trip circuit locks.
In U.S. Pat. No. 3,859,813 of James A. Canter, an ice maker control circuit is disclosed utilizing a mercury thermostat switch responsive to a preselected buildup of the ice slab to stop operation of the water pump and initiate operation of the defrost cycle of the ice maker. The control further provides means for sensing the release of the ice slab under the ice cutting grid so as to effect initiation of a subsequent ice making cycle.
Ko Toya, in U.S. Pat. No. 3,977,851, shows an automatic electronic ice making control system for automatic ice making machines utilizing a thermistor and a differential amplifier including a variable resistor having the same characteristics as the thermistor for compensating the characteristics of the thermistor in accordance with atmospheric ambient temperature changes. Thus, the control is arranged to terminate production of ice independently of the temperature conditions and, thus, seasonal variations in the ambient surroundings of the ice maker.
In U.S. Pat. No. 3,988,903, Jimmy Milton Brewer et al show a dual acting defrost system for ice makers having a solid state switching control responsive to the water level sensing means at a discharge outlet of the evaporator.